The research objectives in this proposal are concerned with the investigation of DNA provirus of the reticuloendotheliosis virus (REV). REV is a prototype virus to study the virus-induced cell transformation. Unlike other leukosis viruses, REV is highly virulent; its incubation period is short; mortality approaches 100%; it has a wide host range; and it is easy to obtain hundreds of milligram quantities of virus from REV-transformed chicken bone marrow cells. The method to be used includes: (1) isolation and characterization of unintegrated infectious DNA provirus from the virus-infected cells to study the size and conformation of DNA provirus, (2) Kinetics of DNA provirus synthesis and integration to study the fate of DNA provirus, (3) cell-free synthesis of infectious DNA provirus and characterization of in vitro product DNA provirus to study the host factor involved in synthesis of infectious DNA provirus, and (4) kinetic studies of unintegrated DNA provirus transfection. So far we have synthesized REV DNA by the endogenous RNA-directed DNA polymerase reaction using either purified REV or ribonucleoprotein complex isolated from the REV-transformed chicken bone marrow cells. The transfecting ability of the DNA products is being investigated.